Loss and Loss Adjustment Expenses - Reconciliation of Beginning and Ending Reserve Balances, Net of Related Amounts Recoverable from Reinsurers (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Roll Forward In Liability For Unpaid Claims And Claims Adjustment Expense [Abstract]
Balance, beginning of period	$ 760,561	$ 772,887	$ 798,409
Less amounts recoverable from reinsurers on unpaid loss and loss adjustment expenses	105,707	95,343	107,216
Net balance, beginning of period	654,854	677,544	691,193
Add incurred related to:
Current accident year	222,715	220,710	241,344
Prior accident years	(61,917)	(63,484)	(65,002)
Total incurred	160,798	157,226	176,342
Less paid related to:
Current accident year	52,292	50,113	58,883
Prior accident years	137,348	129,803	131,108
Total paid	189,640	179,916	189,991
Net balance, end of period	626,012	654,854	677,544
Add amounts recoverable from reinsurers on unpaid loss and loss adjustment expenses	119,266	105,707	95,343
Balance, end of period	$ 745,278	$ 760,561	$ 772,887